<?php
header("Content-type:text/html;charset=utf-8");

$username = $_POST['username'];

$password = $_POST['password'];

if(empty($username) || empty($password)){
echo "";

}else{
include "conn.php";

$sql = "SELECT username, password FROM user WHERE username='$username' && password='$password'";

$res = $conn->query($sql);

$no = $res->num_rows;

if(!$no){
echo "123";

}else{
echo "1234"; //就是这里，登录后跳转到首页后怎么让它不显示登录框了，而直接显示登录后的用户名

}

}
?>